The present invention relates to an apparatus and a method for forming a liquid crystal alignment layer with ion beam irradiation.
In a liquid crystal display (LCD), the orientation direction of liquid crystals is controlled by an alignment layer formed on a substrate. A beam of ions is irradiated at a thin film made of polyimide or an inorganic material. A bond between atoms of the thin film is broken to form an alignment layer with ion beam irradiation. Conventionally, as shown in FIGS. 12 (a) and 12 (b), an ion beam 16 is irradiated at a thin film 30 while moving a substrate 28. As will be mentioned later, the ion beam 16 has divergence and masks 12 are designed in such a manner that only the ion beam 16 is irradiated at the thin film 30 through a slit 14 to contribute to the formation of an alignment layer.
The orientation direction of liquid crystals is determined by an angle φ shown in FIG. 13, in other words, an angle between the ion beam 16 projected on X-Y plane (a plane parallel to the substrate 28 and the masks 12) shown in FIG. 12 (b) and Y-axis, and density distribution of the ion beams 16. Moreover, Y-axis is assumed to be an edge 32a of the mask 12 in FIG. 14. The orientation direction is assumed to be an angle between a major axis of liquid-crystal molecules and Y-axis or X-axis when projecting the molecules on the substrate. An angle θ is an incident angle relative to an X-Y plane in FIG. 13.
Actually, ion beams 16 generated from an ion source have divergence. More particularly, the ion source has a number of outlets to emit the ion beams 16 and a plurality of ion beams 16 emitted from the outlets are irradiated in different directions respectively. The ion beams 16 are irradiated at a point on the thin film 30 from a plurality of directions. The ion beams 16 which affect the orientation direction are the strongest in this respect. It is necessary to align the orientation of the ion beams 16 in all points of the thin film 30.
If the above angle φ is different depending on the position of the alignment layer, liquid crystals will not be aligned in a unidirectional manner. This causes irregularity in brightness and color of the liquid crystal display. As shown in FIG. 14, when the ion beams 16a, 16b, and 16c respectively have different angles φ at each of points A, B, and C on the thin film 30, the orientation direction of the liquid crystals becomes non-uniform. Uniformity in orientation direction of the liquid crystals is required to produce liquid crystal displays of high picture quality.